Forward osmosis is known in the art and has been the subject of recent study due to the likelihood of future fresh water shortages and a corresponding increase in demand for cost effective desalinization and water purification technologies. Sea water, brackish water or otherwise contaminated water can be purified by drawing the water (the solvent) through a semipermeable membrane, which rejects the salts and other contaminants (the solutes). This natural, or forward, osmosis approach differs from the widely used reverse osmosis process where the water is forced through a similarly acting semipermeable membrane under pressure. In forward osmosis processes, the water is drawn through the semipermeable membrane using a draw solution. The forward osmosis process does not purify the water. Forward osmosis simply moves the water from one set of solutes to another set of solutes.
A review and summary of forward osmosis technology is provided by Miller and Evens, Forward Osmosis: A new approach to water purification and desalination, Sandia Report SAND2006-4634, July 2006 in which the concept of using retrograde soluble polymer draw solutes is discussed. The process for accomplishing the separation of the solutes from the water is not described.
An ammonia-carbon dioxide based forward osmosis system is described in U.S. Pat. Nos. 7,560,029 and 6,393,295 to McGinnis where the temperature dependent solubility of the solutes is used for partial separation of the solutes from water. The precipitated solutes in disclosed are solid salts and the balance of the separation is achieved with distillation. U.S. patent application Ser. No. 11/632,994 by Collins also describes using the temperature dependent solubility of salts to separate draw solute from water.
U.S. patent application Ser. No. 11/796,118 describes another forward osmosis system that utilizes coated magnetic nanoparticles as a draw solute. PCT WO/2010/107804 describes using magnetic particles as a controllable osmotic agent.
U.S. Pat. No. 5,679,254 to Chakrabarti describes using the temperature dependent solubility of polymers in water to accomplish desalination, although not through forward osmosis.
U.S. Pat. No. 8,021,553 to Iyer describes a system using retrograde soluble polymer solutes and a nanofilter for separation and recovery of the resulting solute micelles from the product water. Iyer specifies draw solutes with both a hydrophobic and hydrophilic component. Iyer also discloses semi-batch recovery of the solutes by collecting the precipitated (or phase separated) draw solute on a nanofilter and recovering the solute by back flushing the nanofilter.
Improved systems and processes for forward osmosis water purification or desalination are herein disclosed.